1. Field of the Invention
This invention relates to superconductor assemblies, specifically, superconductor assemblies wherein a thermally conductive structural substrate carries a thin film superconductor and also forms a containment for a flow of cryogenic fluid.
2. Description of the Prior Art
Superconductive articles such as cables for the transmission of electricity are well known. Until recently, most teaching regarding the use of superconductors was directed to materials providing superconductivity at temperatures near absolute zero. Thus, for example, in U.S. Pat. No. 4,585,696 issued Apr. 29, 1986 to Dustmann et al a superconducting fiber is disclosed in which a base layer of silicon carbide is applied to the surface of a carbon fiber core. The base layer, in turn, carries a superconducting layer said to consist of a niobium carbon nitride or a niobium oxycarbonitride. The superconducting layer is covered by a shell of high purity copper or aluminum. In U.S. Pat. No. 4,341,924 issued Jul. 27, 1982 to Gleim is disclosed a superconductive article comprising an electrically normal conductive metal cable having on the outer surface thereof a layer containing cobalt phthalocyanine and an alkaline metal such as lithium, sodium or potassium. The metal cable is said preferably to be aluminum and is hollow at its core. The layer of cobalt phthalocyanine and alkaline metal is deposited by vacuum deposition and is covered by a material impermeable to air and water vapors and having a high dielectric constant, such as polyethylene. Such cable is said to operate as a superconductor in a cryogenic environment such as that of liquid nitrogen or liquid hydrogen. (The superconductivity of such phthalocyanine based devices at liquid nitrogen temperatures has not been experimentally demonstrated.) A method of manufacturing a composite wire for use in superconducting cables is disclosed in U.S. Pat. No. 3,890,700 issued Jun. 24, 1985 to Diepers et al. The method of Diepers et al comprises cold-drawing a structure comprising a rod-shaped aluminum core and a niobium jacket enclosing the core. The aluminum core/niobium jacket construction is assembled with a drawing aid surrounding the niobium jacket, such as a copper tube. The drawing aid is removed after the cold-drawing operation has produced a solid bond between the niobium and the aluminum. In U.S. Pat. No. 3,781,982 issued Jan. 1, 1974 to Ziemek et al, a superconductor is taught in the form of a tube made from a self-supporting thin sheet with an axial welding seam. Such tube is attached to a separately made carrier, either as an outside envelope or as an inside lining, in either case being in intimate contact therewith. Lead, niobium and some niobium alloys and compounds are disclosed as being known superconductive materials. In the disclosed embodiment of a superconductor layer carried as an inside lining of a carrier pipe, it is taught that the cryogenic fluid can be passed through the interior of the pipe. Yet another design for a cryogenic cable is disclosed in U.S. Pat. No. 3,736,365 issued May 29, 1973 to Bobo et al. The cryogenic cable of Bobo et al is hollow at its core for the passage of cryogenic fluids such as helium. Surrounding the hollow core is an aluminum covering in which are disposed superconductive strands. A metallic thermal screen surrounds the aluminum covering and incorporates axially extending, circumferentially spaced ducts through which also would flow cryogenic fluid. A steel covering surrounds the entire assembly and a thermal insulator separates the thermal screen from the outside steel covering. Variations on this design are disclosed by Bobo et al, all of which are based on a thermal screen with cryogenic fluid-carrying ducts surrounding a central cryogenic fluid-carrying core. In U.S. Pat. No. 3,537,827 issued Jun. 23, 1967 to Benz et al is disclosed a flexible superconductive laminate in which a superconductive layer is bonded between a layer of a non-magnetic, non-superconductive material which has a high yield strength, a relatively high modulus of elasticity and a layer of a non-superconductive material which has a relatively low modulus of elasticity and a relatively low electrical resistance at cryogenic temperatures. The superconductive laminate of Benz et al is said to be more readily formed into coils because of the proportionate thicknesses of the non-superconductive layers. A method of manufacturing a superconductor assembly is disclosed in U.S. Pat. No. 3,514,850 issued Jun. 2, 1970 to Barber et al. In the method of Barber et al at least one ductile superconductor member is positioned in a sheath comprising at least one metal selected from a named group, such as aluminum, silver, etc. The sheath is provided with an exterior formed of a ductile metal which will support the sheath. The assembly is worked to reduce the cross-sectional dimensions of the superconductor member or members, the sheath and the exterior covering. U.S. Pat. No. 3,493,475 issued Feb. 3, 1972 to Neugebauer et al discloses the use of an anodized aluminum mirror substrate as the base for a cryotron. Specifically, it is therein taught to chemically strip the anodic coating of the mirror substrate and then to apply layers of superconducting films and gates sequentially to the stripped surface. The entire structure thereafter can be anodized. Yet another superconductor assembly is disclosed in U.S. Pat. No. 3,327,370 issued Jun. 27, 1967 to Cohen. Specifically, Cohen discloses a process for manufacture of coated superconductive ribbons. The method involves applying to a tin coated ribbon a coating of boron nitride. Boron nitride is suspended in a volatile carrier, e.g. acetone, applied by spraying. According to one embodiment, the niobium, carrying clad tin on one surface, is folded in upon itself such that the niobium sandwiches the tin. The aforesaid boron nitride coating is then applied, the ribbon wound onto a spiral and then heat treated to produce Nb.sub.3 Sn.
In recent years, new superconductive materials have been developed featuring higher critical temperatures than conventional superconducting substances. That is, materials have been discovered which are superconducting at relatively high temperatures, such as that of liquid nitrogen. The higher the critical temperature, the less costly it is to maintain such critical temperature and, accordingly, the superconducting condition of the material. These materials include various oxide compounds, most notably compounds consisting of rare earths, alkali earths and copper oxide. More generally, the new compounds include, but are not limited to, compounds of the system generally represented by (L.sub.l-x M.sub.x).sub.a A.sub.b D.sub.y, as reported by Woo et al in Physical Review Letters 58, No. 9, 908-910 (2 March, 1987). Such so-called "high temperature" superconductors (hereinafter high T.sub.c superconductors) include, for example, Y-Ba-Cu-O ceramic compounds and can be laid down and used in thin film applications including, for example, electronic circuit connector pathways, etc. Such thin film applications, however, require substrates onto which the superconductor can be deposited plus means for maintaining the needed cryogenic temperatures so that the thin film superconductor can be maintained in a superconducting state. Certain uses of the new ceramic superconductors in thin film applications require an assembly providing the needed thermal conditions, electrical isolation and structural support, the ceramic itself making little or no contribution to the stuctural support. It is an object of the present invention to provide such an assembly. Additional objects of the invention will be understood by the skilled of the art in view of the following disclosure.